The present invention relates to a process for preparing superabsorbent-containing composites having an improved efficacy in the handling of a complex fluid. More particularly, the present invention relates to a process for preparing superabsorbent-containing composites capable of selectively removing at least a portion of an amount of at least one specific component of a complex fluid.
Superabsorbent materials possess a number of attributes that make them attractive in many different applications. As a result of their superior water-absorbing attributes, superabsorbent materials have supplanted much of the traditional absorbents in disposable diapers and have made significant improvements in the performance of disposable feminine hygiene products and disposable adult incontinence products. The basic property of water absorption has suggested the use of superabsorbent materials in many other applications, including paper towels, surgical sponges, meat trays, disposable mats for outside doorways and in bathrooms, and for household pet litter, bandages and wound dressings.
The largest use of superabsorbent materials, however, is in disposable personal hygiene products. These products include, in order of volume of superabsorbent material used, diapers, training pants, adult incontinence products and feminine hygiene products. Of these, diapers accounted for over 90% of the total superabsorbent material sold in 1995. Because of this, the development of superabsorbent properties in general has been focused on optimizing absorbency of urine.
A challenge for the developers of products into which superabsorbent materials are incorporated, however, is the very significant difference between the fluids to be absorbed by the various disposable absorbent products. With diapers, for example, the fluid is typically urine, a simple fluid of primarily water, salts and nitrogenous materials such as urea. With feminine hygiene products, for example, the fluid is typically menses, a complex fluid including water, salts, and cells. In such complex fluids, the cells are far too large to diffuse into the network structure of the superabsorbent material, and may instead adsorb onto the surfaces of the particles of superabsorbent material. The high osmotic pressure of partially swollen superabsorbent material can de-water the cells if they are in direct contact and this can lead to a nearly impermeable surface layer of cells surrounding the superabsorbent material, resulting in a severe reduction in the efficacy of the superabsorbent material. These factors suggest that the nature of the superabsorbent material for absorbing complex fluids such as menses should be different from the superabsorbent material used for absorbing simple fluids such as urine. As a result of this suggestion, various approaches have been disclosed regarding the development of superabsorbent materials capable of absorbing complex fluids such as menses.
A number of these approaches disclose that superabsorbent material suitable for absorbing simple fluids may be chemically treated to enhance its ability to absorb complex fluids. While considered as being somewhat effective, these approaches at times provide for complicated manufacturing processes, which invariably increase the cost of the resulting superabsorbent material. In addition, it has been found that some of these approaches tend to increase the possibility of the user being exposed to harmful contaminants during use.
As an alternative to the foregoing chemical treatment of superabsorbent material, other approaches have focused on the development of superabsorbent materials specifically designed to absorb complex fluids. Unfortunately, any improvement in the ability of these specifically designed superabsorbent materials to absorb complex fluids is oftentimes offset by a diminishment in their ability to absorb simple fluids. Moreover, these specifically-designed superabsorbent materials are relatively expensive compared to the cost of mass-produced superabsorbent materials developed primarily for absorbing simple fluids such as urine.
The present inventors have recognized the difficulties and problems inherent in the prior art and in response thereto conducted intensive research in developing a process for preparing superabsorbent-containing composites having an improved efficacy in the handling of complex fluids. Despite factors suggesting to the contrary, the present inventors surprisingly found that a mass-produced, readily obtainable and affordable superabsorbent material, developed primarily for absorbing simple fluids such as urine, can be incorporated into a superabsorbent-containing composite capable of selectively removing at least a portion of an amount of at least one specific component of a complex fluid. Due to the use of mass-produced, readily obtainable superabsorbent materials in relatively uncomplicated manufacturing processes, the superabsorbent-containing composites prepared according to the present invention are relatively inexpensive when compared to the cost of superabsorbent materials specifically designed to absorb complex fluids. While demonstrating an improved efficacy in the handling of complex fluids, the superabsorbent-containing composites prepared according to the present invention surprisingly do not demonstrate any significant diminishment in ability to absorb simple fluids. In addition, the superabsorbent-containing composites prepared according to the present invention do not expose the user to harmful contaminants during use.
In one embodiment of a process for preparing a superabsorbent-containing composite, at least one particle of at least one coating material is introduced into a flowing gas stream. The flowing gas stream moves the coating material through a zone where an association agent is applied to the coating material. Next, at least one particle of at least one superabsorbent material is introduced into the flowing gas stream. Thereafter, the flowing gas stream is maintained until the superabsorbent material is covered with at least a first layer of the coating material. The coating material is in intimate association with and covering the surface of the superabsorbent material.
In another embodiment of a process for preparing a superabsorbent-containing composite, at least one particle of at least one superabsorbent material is introduced into a flowing gas stream. The flowing gas stream moves the superabsorbent material through a zone where an association agent is applied to the superabsorbent material. Next, at least one particle of at least one coating material is introduced into the flowing gas stream. Thereafter, the flowing gas stream is maintained until the superabsorbent material is covered with at least a first layer of the coating material. The coating material is in intimate association with and covering the surface of the superabsorbent material.
In still another embodiment of a process for preparing a superabsorbent-containing composite, at least one particle of at least one coating material and at least one particle of at least one superabsorbent material are introduced into a flowing gas stream. The flowing gas stream moves the coating material and superabsorbent material through a zone where an association agent is applied to the coating material and the superabsorbent material. Thereafter, the flowing gas stream is maintained until the superabsorbent material is covered with at least a first layer of the coating material. The coating material is in intimate association with and covering the surface of the superabsorbent material.